This invention relates to the field of electrochemistry and, more particularly, to electrodeposition of metals.
The ground test accelerator program at Los Alamos National Laboratory utilizes a radio frequency quadrupole (RFQ) through which a particle beam passes. A large quantity of RF power is added to this RF cavity, which is operated at cryogenic temperatures (20-50 K.). It is desirable to fabricate the RFQ of aluminum having a thin coating of copper. However, the coefficient of thermal expansion of aluminum is different from that of copper, so that cooling an aluminum article having a copper coating from room temperature to a cryogenic temperature and back to room temperature promotes delamination at the aluminum/copper interface. The present invention provides a solution to this delamination problem and will be useful in other applications where good adhesion of a copper layer to a substrate is required.
Aluminum articles having dimensions similar to those of components of the RFQ were coated with thin layers of copper by prior art electrodeposition processes and subjected to cycling between room temperature and the temperature of liquid helium (35 K.). It was observed that the copper layers separated from the aluminum substrates. Bubbles formed on the surface of the copper and the copper layer detached from the aluminum at the edges of the articles, even though no mechanical stresses were applied to the coated test articles. Thus, it was necessary to develop a process which provides better adherence between a substrate and a layer of electrodeposited copper. Articles which were copper coated using the process did not delaminate when subjected to cycling between room temperature and 20 K. and scratch and peel tests did not result in separation of the copper layer from the substrate.